You've struck a tricky topic here! I can't claim to be authoritative, but my reading of the situation (including the new provisions in the Localism Act) is that a council is required to set up a company where it is embarking on a commercial enterprise.
My impression is that the acid test is not whether a profit is made, or may be made, but whether the council is engaging in the activity from purely commercial motives.
In other cases, such as when a council is trying to offset the cost of a service, then it appears that the obligation to set up a company does not apply. Clearly there is a fuzzy boundary here, but it seems unlikely that a council would be taken to task over small sums or windfall profits.